Evolution of a Range-boundary Thrust in a Strike-slip Fault System: The Late Miocene-recent Slip History of the McCallum Creek Fault, Eastern Alaska Range, Alaska.

摘要

The McCallum Creek thrust system consists of the McCallum Creek fault and a kinematically linked foreland blind thrust system that splay south from the Denali fault in the eastern Alaska Range. Apatite fission track cooling ages, tephrachronology, and balanced cross sections indicate that convergence partitioned to the McCallum Creek thrust system from the Denali fault has accommodated 3.3-3.6 km of rock exhumation resulting in 4.6-5.3 km of shortening directed toward ∼005-185 since hanging wall samples passed through apatite fission track closure at ∼6 Ma. Thrusting on the main McCallum Creek fault resulted in deposition of foreland strata in the footwall broadly coeval with apatite fission track cooling ages in the hanging wall of the fault. The blind foreland thrust system developed after ∼3.7 Ma and was subsequently overtaken by out-of-sequence slip on the main McCallum Creek fault. Incised segments of modern streams and tilted Quaternary deposits suggest that foreland structures are the most recently active part of the thrust system. Shortening on the McCallum Creek fault results in internal contraction of the Southern Alaska Block and advocates for a combined rotational and indenter model for Southern Alaska Block motion. The onset of thrusting in the McCallum Creek area likely records a far-field response to plate-kinematic adjustments in the Alaska syntaxis at ∼6 Ma.